This invention relates to a magnetically driven centrifugal pump.
Generally, this type of pump conprises a sealed housing having a chamber formed therein, an external rotor rotatably disposed outside the housing and having a plurality of permanent magnets, an internal rotor rotatably retained by a shaft provided within the housing and having a plurality of permanent magnets, and an impeller rotatably retained by said shaft. That impeller chamber section of said chamber which has the impeller received therein is connected to that rotor chamber section of said chamber which has the internal rotor received therein, so as to permit the free passage of a fluid between both sections. The shaft is supported at both ends, respectively, by an inner wall of the rotor chamber section and a spider member provided for the impeller chamber section. Bearing members for the shaft are cooled by the fluid flowing thereto from the impeller chamber.
This type of conventional pump has the following drawbacks.
A. Since the impeller chamber section is directly connected to the rotor chamber, the mutually opposite axial thrusts acting on the impeller are difficultly balanced. Further, since, in the case of high pressure being produced within the impeller chamber section, this pressure directly acts on the wall of the rotor chamber, this wall should be formed thick and firm. This runs counter to the specific demand that the wall of the rotor chamber section must be formed as thin as possible for purpose of passing magnetic flux therethrough.
B. Since the spider member supporting the shaft is provided at the inlet side of the impeller chamber section, cavitation occurs within the impeller chamber section, so that the cooling efficiency of the shaft bearing section is decreased simultaneously with production of noises and occurrence of vibration. Further, the shaft must be so designed as to have a large span. This is very disadvantageous for this type of pump since the shaft must be formed or inorganic material such as Al.sub.2 O.sub.3 in order to have high corrosion resistance.
Accordingly, the object of the invention is to provide a magnetically driven centrifugal pump in which mutually opposite axial thrusts can be readily balanced and which can be prevented from damaging the wall of the rotor chamber.
The magnetically driven centrifugal pump according to the invention comprises a split plate for dividing a space within a sealed housing into two parts-impeller chamber and motor chamber, a passage means for guiding a fluid within the impeller chamber into the rotor chamber, and a restricting means disposed in the passage means to reduce the fluid pressure within the passage means. A shaft retaining the rotor and impeller is extended through the slit plate and is rotatably supported by a bearing member provided for the inner wall of the rotor chamber and a bearing member provided for the split plate.
The pressure within the rotor chamber is maintained always lower by the restricting means than that within the impeller chamber. Within the rotor chamber, the mutually opposite axial thrusts acting on the rotor are balanced depending upon the relationship between the forward and rearward regions of the rotor. Within the impeller chamber, the mutually opposite axial thrusts acting on the impeller are balanced depending upon the relationship between the forward and rearward regions of the impeller. In this way, the balance between the axial thrusts within the rotor chamber and the balance between the axial thrusts within the impeller chamber are independently achieved, so that all axial thrusts can be readily balanced. For instance, even where, upon a rapid stop of the pump, a so-called water hammer phenomenon occur within the impeller chamber, this phenomenon is weakened by the restricting means to have no direct effect upon the interior of the rotor chamber. For this reason, the peripheral wall of the rotor chamber can be formed relatively thin, whereby the efficiency of the magnetic connection between an internal rotor within the rotor chamber and an external rotor outside the same can be increased.
The shaft is supported by the bearing members at its rearward end portion and its intermediate portion, respectively. Accordingly, the shaft portion between the bearing members becomes shorter than in the case of the conventional shaft supported at its both forward and rearward ends. Therefore, a stress acting on the shaft becomes small to decrease possible damages to the shaft. Further, since the present invention eliminates the necessity of providing the conventional spider member supporting the forward end of the shaft, cavitation is less likely to occur within the impeller chamber, whereby to increase the life of the pump and the cooling efficiency of the shaft-supporting sections.